Does coffee go bad?

The term "Green coffee bean" refers to unroasted mature or immature coffee beans. These have been processed by wet or dry methods to remove the outer pulp and mucilage and have an intact wax layer on the outer surface.

When mature, they have a brown to yellow or reddish color and typically weigh 300 to 330 mg per dried coffee bean. Nonvolatile and volatile compounds in green coffee beans, such as caffeine, deter many insects and animals from eating them. Further, both nonvolatile and volatile compounds contribute to the flavor of the coffee bean when it is roasted. Nonvolatile nitrogenous compounds and carbohydrates are of major importance in producing the full aroma of roasted coffee and for its biological action. When green coffee beans are roasted, other molecules with the typical pleasant aroma of coffee are generated, which are not present in fresh green coffee.

Many consumers experiment with creating green bean "Extract" by steeping green coffee beans in hot water. Often, the recommended times of steeping extract too much caffeine to provide a pleasant taste. The alkaline stock base that results can be paired with acidic or fruity extracts, with or without sweetener, to mask the vegetable-like taste of the extract.

During roasting, the major part of the unpleasant-tasting volatile compounds are neutralised. Unfortunately, other important molecules such as antioxidants and vitamins present in green coffee are destroyed. Carbohydrates make up about 50% of the dry weight of green coffee beans. The carbohydrate fraction of green coffee is Droste by polysaccharides, such as arabinogalactan, galactomannan, and cellulose, contributing to the tasteless flavor of green coffee.

Arabinogalactan makes up to 17% of dry weight of green coffee beans, with a molecular weight of 90 kda to 200 kda. Free monosaccharides are present in mature brown to yellow-green coffee beans. The free part of monosaccharides contains sucrose (gluco-fructose) up to 9000 mg/100g of arabica green coffee bean, a lower amount in robustas, I.E. 4500 mg/100g. Mannitol is a powerful scavenger for hydroxyl radicals, which are generated during the peroxidation of lipids in biological membranes. Trigonelline (n-methyl-nicotinate) is a derivative of vitamin b6 that is not as bitter as caffeine.

In green coffee beans, the content is between 0.6% and 1.0%. At a roasting temperature of 230 °c (446 °f), 85% of the trigonelline is degraded to nicotinic acid, leaving small amounts of the unchanged molecule in the roasted beans.